The present invention relates generally to a guide rail or tensioner arm for guiding or tensioning a drive chain and more particularly to a sheet metal bracket with tabs formed on one edge which are bent in alternate directions for engagement with a plastic shoe or wear face. The guide rails or tensioner arms of the preferred embodiment of the present invention are designed for use as chain guides or tensioner arms in power transmission systems and engine timing systems using chain to drivingly connect the elements of the system.
Conventional engine timing systems include a crankshaft and a corresponding sprocket system which operates an engine with either a single or dual overhead camshafts. The operation of the system is based upon a chain which extends from the crankshaft to the camshaft (or camshafts) and returns to the crankshaft in an endless loop. Rotation of the crankshaft and the chain causes the camshaft to rotate.
Examples of engine timing systems are shown in U.S. Pat. No. 5,427,580, which is incorporated herein by reference. As the chain extends in an endless loop between the driving and the driven sprockets, such as those located on a crankshaft (driving) and camshaft (driven), the chain forms a "tight" side and a "slack" side. The tight side is formed by the tension in the span of chain between the links entering the driving sprocket and the links leaving the driven sprocket. A slack side is formed on the other span of chain between the links leaving the driving sprocket and entering the driven sprocket.
The performance and action of the chain can differ dramatically between the tight and slack sides. A chain tensioner is conventionally used on the slack side of the chain. The tensioner acts to take up or eliminate the slack in the chain. As the engine accelerates or decelerates, the tensioner arm may move closer to the chain to maintain the tension, i.e., reduce the slack in the chain. The tensioner arm typically includes a convex surface to match the path of the chain.
In contrast, a chain guide is conventionally used on the tight side of the chain. Such a guide does not include a tensioner piece, as the chain portion remains tight between the two sprockets. Typically, the guide is fixed to a mounting surface, such as a side of the engine block. The guide serves to maintain the desired path of the chain between the sprockets.
Conventional guide rails of the prior art may be formed as a single piece but more typically include two components, a bracket or carrier and a plastic shoe or wear face, that are produced independently of one another and interconnected by some form of locking device. The bracket may be made of metal or plastic and the wear face or shoe is typically made of plastic.
U.S. Pat. No. 4,832,664 discloses a guide rail that includes a carrier formed of a first plastic material and a slideway lining body made of a second different plastic material. Each of these two components is formed in a mold. The carrier and slideway lining body are interconnected to one another by dovetail connections, and secured by bent end sections. In the chain guide shown in U.S. Pat. No. 4,832,664, the carrier and sliding guideway body are formed on complementary dovetail cross-sections, and interlocked by the bent end section, or a similar meshing arrangement, that prevent relative movement between the two portions.
U.S. Pat. No. 5,813,935 discloses a guide rail where the wear face is produced by an extrusion molding process. The extrusion molding process is used in place of injection molding to permit the use of dovetail connections and provide interlocking components. The carrier portion is substantially an I-shape in cross-section with an extending dovetail section. The dovetail section on the carrier fits a complementary dovetail cross-section formed in the wear face. The carrier portion may be manufactured of die cast aluminum or magnesium; injection molded nylon; steel stamping; steel casting; or, steel or aluminum weldment.
Prior art brackets for chain guides, when made of metal, have often been formed with the bracket mounted to the engine at a location away from the chain centerline. FIG. 1 shows such a chain guide. The bracket is L-shaped in cross-section One side of the bracket 12 is mounted to an engine block 14 and the other side of the bracket 12 includes an attached shoe 16 with a channel shaped wear face 18. The chain 20 passes along the channel shaped wear face 18. The load applied to the bracket 12 by the chain 20 acts through distance "X" applying a stress to the bracket. To prevent the bracket 12 from bending or failing due to the stress, a bracket of thick material is used or an expensive stronger material is used.
The guide or tensioner arm of the present invention includes a carrier or bracket made from a formed sheet metal stamping. On a longitudinal edge of the bracket a series of extending tabs are formed. The tabs are bent perpendicular to the main body of the bracket in an alternating fashion. This forms a bracket which has a T-shape providing a base for mounting a plastic shoe with a wear face for guiding a chain.